Abstract
A new passive device for mitigating cable vibrations is proposed and its efficiency is assessed on 45-meter long taut cables through a series of free and forced vibration tests. It consists of a unilateral spring attached perpendicularly to the cable near the anchorage. Because of its ability to change the cable dynamic behaviour through intermittent activation, the device has been called state switched inducer (SSI). The cable behaviour is shown to be deeply modified by the SSI: the forced vibration response is anharmonicc and substantially reduced in amplitude whereas the free vibration decay is largely sped up through a beating phenomenon. The vibration mitigation effect is mainly due to the activation and coupling of various vibration modes, as evidenced in the response spectra of the equipped cable. This first large-scale experimental campaign shows that the SSI outperforms classical passive devices, thus paving the way to a new kind of low-cost vibration mitigation systems which do not rely on dissipation.
Highlights
Resonances of slender structures such as bridges, towers, or cables are usually mitigated by dampers of various types or/and dynamic absorbers [1,2,3,4,5,6,7]
The state switched inducer (SSI) is a unilateral spring which slightly stiffens in an intermittent way the structure it is connected to
An experimental campaign conducted on two fullscale cables has shown that SSI devices reduce significantly the steady state vibration amplitude under forced vibrations and shorten drastically the free decay period
Summary
Resonances of slender structures such as bridges, towers, or cables are usually mitigated by dampers of various types or/and dynamic absorbers [1,2,3,4,5,6,7]. This property naturally yields a positive effect of the SSI: according to the Parseval theorem, conservative systems receiving the same input energy have the same integral in the frequency domain; if peaks are more numerous for the nonlinear oscillator, their amplitude and the resonances are smaller than those for the corresponding linear oscillator Another interesting property of the SSI is the sudden change of dynamic state at the switch time. Cable resonances are mainly due to parametric excitations through the anchorage motion or to direct excitations by a combination of wind and rain In both cases, the loading, usually assumed harmonic, can last from some seconds to one minute and is followed by a free decay period. These three cable configurations are, respectively, referred to as “SSI cable,” “free cable,” and “restraint cable.”
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